What do you say to movies like John Carter, Watchmen and Green Lantern? Guardians of the Galaxy won't be the 1st scifi/action live action to underperform at the box-office and right now, I don't think it will perform really well at the box-office.

Well this does come with the assumption that GotG will be 'good'. All three of those films you listed sucked so it's no wonder they all bombed.